1. Field of the Invention
This invention relates in general to micro-switches and, more particularly, to a micro-machined bistable switch using a shape memory alloy.
2. Description of the Related Art
The first electro-mechanical and solid state micro-switches were developed in the late 1940's. Since that time, the electronics industry has pushed the manufacturing and functional limits for producing such switches. In particular, current electro-mechanical micro-switches exhibit technical inadequacies in size, cost function, durability, and connection techniques for high frequency applications. In turn, solid state switches exhibit a characteristically high off-state to on-state impedance ratio, and for many applications, undesirably high values of on-state "contact" resistance in off-state coupling capacitance. Consequently, the electronics industry is currently looking into new and innovative ways to manufacture switches that can be smaller, more reliable, durable, functional, and cost efficient.
In a variety of present day and predicted circuit applications, a need exists for low cost, micro-miniature switching devices that can be fabricated on conventional hybrid circuit substrates or boards and have bistable capabilities. In addition, the manufacturing process for these devices should be compatible with conventional solid state techniques such as thin-film deposition and patterning procedures used to form the conductive paths, contact pads and passive circuit elements included in such circuits.
A shape memory alloy ("SMA") is a known material capable of undergoing plastic deformation from a "deformed" shape to a "memory" shape when heated. If the SMA material is then allowed to cool, it will return partially to its deformed shape and can be fully returned to the deformed shape. In other words, the SMA material undergoes a reversible transformation from an austenitic state to a martensitic state with a change in temperature.
Research and development companies have only touched the surface of how this controllable shape deformation material can be used in switching structures. For example, conventional electro-mechanical switches have used SMA wires as a rotary actuator and bent SMA sheets as a valve. The wire is twisted or torsioned about its longitudinal axis and the ends of the wire are then constrained against movement. The sheet actuators are mechanically coupled to one or more movable elements such that the temperature-induced deformation of the actuators exerts a force or generates a motion of the mechanical elements.
The problems with these and similar SMA switch configurations and manufacturing techniques are similar to those described above for conventional electro-mechanical switches. In particular, constraints of size, reliability, durability, functionality, and cost limit the usefulness of prior art SMA switches.
In closing, conventional switches and relays, with or without the use of shape memory alloys, are normally large, bulky, or too fragile to be used for industrial purposes or mass production. Therefore, it would be advantageous to develop a switch or relay that can benefit from the characteristics of a shape memory alloy and eliminate the problems listed above of current switching technologies that may or may not use a shape memory alloy.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.